NREM Sleep Duration, Fast Spindles, and Face Recognition Memory

Non-rapid eye movement (NREM) supports episodic memory consolidation, but its contribution to face recognition tasks remains unclear. We examined whether a short nap and its electrophysiological characteristics influenced lineup performance. Thirty-five participants encoded ten unfamiliar faces and then completed either a 40-minute nap followed by 30 minutes of quiet wakefulness (n = 14) or 70 minutes of quiet wakefulness (n = 21). They subsequently performed ten target-present lineups. Recognition accuracy, false identifications, and incorrect rejections did not differ between groups. Within the sleep group, greater total NREM (N2+N3) sleep duration was associated with fewer correct identifications, an effect that remained significant after correction for multiple comparisons. Conversely, greater fast spindle power during N3 was associated with more correct identifications, although this relationship did not survive correction. No other sleep stage or oscillatory measure was significantly related to performance. These findings suggest that a short nap does not generally improve face recognition, but that the duration of individual sleep stages and specific aspects of sleep microstructure may have distinct and potentially opposing associations with performance. The negative association with NREM duration may reflect sleep inertia, whereas fast spindle activity could contribute to the consolidation of facial representations.